dma-ranges null and not present not well defined

[wmamills]

If a node has ranges but not dma-ranges what should be done?

• assume same translation as ranges? assume 1:1 translation?

Likewise is dma-ranges is present but has no value, does that mean direct mapped even when there is a ranges present?

[robherring]

While 'ranges' is required to translate and define memory mapped addresses, 'dma-ranges' is optional (or forgotten). Missing is 1:1 translation.

The translation is a bit different too. For 'ranges', a DT could have 1:1 translation or make the child nodes a relative offset and the result is the same. For dma-ranges, the cpu address, bus address and addressable size are all important to the software.